With funding from check-off dollars from the Iowa Soybean Association, we have evaluated the effect of commercially available fungicide and insecticide seed treatments. We evaluated seedling diseases, insects, and yield of soybean in Iowa in 2012. This field study was done at three locations in Iowa: ISU Northeast Research and Demonstration Farm (NERF), Nashua; ISU Southeast Research and Demonstration Farm (SERF) near Crawfordsville; and a farmer’s field in Nevada (two planting dates). Soybean variety varied by location. Seed treatments were professionally applied by the respective companies. Varieties are commercially available, but their information will not be disclosed.

Materials and methods

The experimental design at each location was a randomized complete block with four replications. Plot sizes were 10 ft-wide (four rows) by 17.5 ft. Planting and harvesting dates are listed in Table 1, and the seed treatments included are listed in Table 2. In addition, the effect of a seed treatment plus a foliar application of Headline (6 oz/A) + Leverage 360 (3.8 oz/A) applied at beginning pod set (R3) on yield was compared. Seedling disease and insect damage were assessed at 14 days after planting (dap) and 28 dap. One-meter stand counts were taken 14 and 28 dap, and vigor (plant height) was assessed 28 dap. Foliar and stem disease was assessed at growth stage R5/R6. Only diseases that were greater than one percent severity were recorded. Soybean aphid populations were assessed at growth stage R1 and R3 to R4.5. Plots were harvested with a plot combine. Grain moisture at harvest was determined and yields were converted to bu/A at 13 percent moisture.

Results

The 2012 growing season was extremely hot and dry. No seedling disease or insect (bean leaf beetle, soybean aphid) damage occurred in any of the four trials. Similarly no foliar or stem diseases were observed.

No differences in stand counts were detected at either 14 dap or 28 dap in three of the four trials. At the early planting date at Nevada, stand counts at 28 dap for the Poncho + VOTiVO, Pioneer premium and Inovate + Metastar treatments greater than the control (untreated seed) (P<0.1).

Yield varied across locations and ranged from 54.6 to 74.9 bu/A in the untreated control (Table 2). There was evidence of an effect of seed treatment on yield at three of the four sites (P<0.1). At SERF (Crawfordsville), the yield of soybean treated with either CruiserMaxx + Avicta, CruiserMaxx Plus or Inovate were greater than the untreated control (71.7 bu/A, 70.6 bu/A and 70.1 bu/A, respectively versus 67.1 bu/A). In the early planting date trial at Nevada, the Inovate + Metastar yielded less than the untreated control (69.6 bu/A versus 74.9 bu/A). At NERF (Nashua), Cruiser Maxx + Avicta (58.7), Pioneer Premium (60.9 bu/A) and Inovate + Metastar (58.9 bu/A) yielded greater than the untreated control (54.6 bu/A). At three of the four locations, application of Headline + Leverage at R3/R4 resulted in higher yields for some treatments (P<0.1; Table 2).

Summary

The benefit of a seed treatment on soybean stand establishment was not evident in our 2012 field trials. Much of the research across the Midwest has shown that seed treatments only protect soybean stand when cold (<55F), wet conditions occur within a few days of planting. In addition, we do not expect to see yield protection in the absence of significant pest pressure. We did, however, detect evidence of an effect of seed treatment on yield at three of our four sites, although no one product stood out above the rest. A tremendous amount of research on the biology of soybean seedling diseases in the Midwest is currently being done with funding from USDA-NIFA, the United Soybean Board, and the North Central Soybean Research Program. The Iowa Soybean Association is also funding research in Iowa. The goal of this research is to improve our understanding of the pathogens that are causing seedling disease and the conditions that favor infection and disease development both early in the growing season and as the season progresses. The sensitivity of these pathogens to fungicides used in seed treatment products is also being evaluated. These data may help to explain why one seed treatment benefits yield at one location and not necessarily at another.

Acknowledgements

Funding for this study was provided by Iowa Soybean Association. We thank Bayer CropScience, Syngenta and Valent for treating seed for the study.